Bus oriented bi-directional audio/video interconnection systems are known and used, for example, for interconnecting component audio/video apparatus such as video tape recorders, video disc players, television tuners, video cameras, video monitors and the like. In typical systems, a common bus containing control, audio and video signals is "daisy chained" between various equipment and driven by tri-state drivers so that the bus may be "shared", so to speak, by all of the connected audio/video units. Such a system is described, for example, by Beyers, Jr. in U.S. Pat. No. 4,581,645 entitled DISTRIBUTED SWITCHED COMPONENT AUDIO/VIDEO SYSTEM which issued Apr. 8, 1986.
More recently, the U.S. Electrical Industries Association (EIA) has considered standardization of audio, video and control interconnections for television apparatus. One standard under consideration proposes audio and video interconnection using twisted pair cables driven by tri-state balanced line drivers. Devices are connected in "daisy chain" fashion to the bus which is terminated with 120 Ohm loads at the first and last devices and with intermediate devices having relatively high impedance inputs connected for bridging operation. An example of such a system is described by White et al. in allowed U.S. application Ser. No. 08/294,146 entitled TRI-STATE VIDEO DIFFERENTIAL DRIVER filed 8 Aug. 1994.
Significant parameters of the audio bus receiver portion of the proposed standard includes (i) a bus audio differential signal level of 2.0 volts RMS (plus or minus 20%), (ii) a bus receiver common-mode range of 5.0 volts (plus or minus 2.0 volts DC), (iii) a minimum input impedance (with the receiver device on or off) of 3K Ohms differential, DC-20 kHz and 1.5K Ohms common mode and (iv) a common mode rejection ratio of 60 dB.
To meet these requirements one might consider the use of conventional techniques such as providing a stand-by power supply or precision attenuation networks (to provide the desired bus isolation under power-down conditions) and selecting feedback controlled operational amplifiers to meet the gain and common mode requirements and to provide single-ended to differential conversion. However, combining such conventional techniques can result an overall receiver design that may be prohibitively costly and overly complex for use in mass produced consumer products such as VCR's or television receivers.